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Consideration of Roadside Design and Roadside Features in the Highway Safety Manual

In the project development process, transportation engineers assess the effect of roadside designs and features on crashes. The <em>Highway Safety Manual</em> (HSM) provides scientifically sound information to support this decision making through accident modification factors (AMFs), which analyze the safety effect of specific design elements known to have an influence on the frequency or severity of crashes. Few roadside AMFs exist, and those that do are not typically of the statistical quality deemed appropriate for inclusions in the first edition of the <em>Highway Safety Manual</em>. The <em>Roadside Design Guide</em> (RDG) provides a probability of encroachment model to quantify the safety of a roadside design and compare the design against other designs. Software support for the HSM is provided through the IHSDM CPM and through RSAP for the RDG. This project will review the two methods; document inconsistencies in predicting the frequency and severity of run-off-road crashes; update the models to provide consistency and provide guidance to practitioners on the successful implementation of each method at various planning, highway design, and operations stages; explore the possibility of incorporating RSAP with the IHSDM; and identify a critical set of AMFs that would support the quantification of changes to the roadside and the installation or modification of roadside features at the identified stages of the project development process, eliminating the need for the use of subjective hazard ratings. This project will develop these AMFs for inclusion in a future edition of the <em>Highway Safety Manual</em>. It is expected that the methods used to develop these AMFs will meet the scientific protocol acceptable for inclusion in the <em>Highway Safety Manual</em> and FHWA AMF clearinghouse as an excellent quality AMF. The development of the improved roadside AMFs has data needs met from the NCHRP Project 17-22 and 17-43 databases and other identified databases. An outcome of this project will be improved roadside safety decision-making tools for transportation agencies. PHASE 1, Comparison of RDG and HSM Tasks: (1) Conduct a literature review of the development of the HSM, the RDG, RSAP, and the IHSDM methods for the analysis of roadside crashes used by these two different approaches. (2) Survey practitioners, researchers, design consultants, and transportation agencies to assess the current needs as they relate to roadside safety during the planning stage, the design stage, and the management of assets. The survey shall also ask for input about specific roadside concerns or areas of need regarding more AMFs. (3) Identify a minimum of five example problems for analysis using the two methods. (4) Document inconsistencies between the two methods and opportunities to provide consistency through updating data sources, base models, or modification factors. (5) Assess available data sources from completed and ongoing NCHRP projects, as well as other state and federal research or databases. Possible data sources include NCHRP 17-22 and 17-43. (6) Develop a prioritized list of roadside AMFs which should be evaluated for development and inclusion in future versions of the HSM. (7) Review RSAP and IHSDM methods and coding for the possible inclusion of RSAP as a module in the IHSDM. (8) Recommend if it's appropriate to consider both methods for continued parallel development for the safety assessment of the roadside or if one method should be chosen for future development efforts. (9) Document findings in an interim report. The report shall include guidance based on the findings of this phase, about the appropriate inclusion of each analysis method into the planning and design process as well as the life-cycle management of the highway network. PHASE 2, Development of Roadside AMFs Tasks: (1) Review the protocols for <em>Highway Safety Manual</em> AMF development. (2) Develop AMFs for the base conditions outlined in parts C and D of the <em>Highway Safety Manual</em>. AMFs shall be developed using the data available from the 17-22 and 17-43 projects as well as other identified sources. Additional data gathering is not anticipated. The prioritized list of AMFs developed in phase 1 shall be reviewed in consultation with the panel. A list of AMFs for development under this project will be produced based on the data available. (3) Develop a list of additional data needs for the NCHRP 17-43 "Ongoing Data Collection" panel's or other data collection projects' consideration of inclusion. (4) Depending on the outcome of phase 1, task 8, inclusion of these findings may be necessary in the RSAP encroachment model as well. (5) Document findings in a final report. This research will provide a document which will supplement the soon-to-be-released HSM and the existing RDG as a means to determine under which circumstances the designer should employ which method to predict crashes, evaluate the potential benefit of safety improvements for the roadside, and provide more AMFs to supplement those provided in the first edition of the HSM. The urgency is high since there is potential for introducing considerable confusion to the design profession by having two methods for similar purposes that may yield conflicting results. Furthermore, the First Edition of the HSM does not provide AMFs to address most of the typical changes of roadside designs and features that agencies currently undertake and subsequently does not support the quantification of the effect of the roadside on crashes and crash severity within the project development process.<p> </p>